What is “normal labor”? That’s a tough question. The answer probably lies within the answer to another question, “What is a normal human being?” In an effort to define normal labor, an overly simplistic model has emerged. The model is good enough, however, to frame the issue. However, remember, when scientists look for ways to describe the events of large populations, they think about “averages” (or “means”). And when scientists describe “means”, they talk about “variance from the mean”. Variance from the mean is the allowance that is made to explain the individual variations to “normal” (or average, or the mean) which are deemed close enough.
There are many factors involved in any one woman’s labor experience which might explain why her labor is not quite average or normal, but may be good enough to get the job done. Midwives and doctors talk about “protractions” and “arrests” to explain these deviations (or variances) from the average. A protraction is a slowing down of the progress of labor, and an arrest is when progress stops completely.
As you read about labor, allow some latitude for these individual variations. Patience is often a virtue in this business. If a mother and fetus are healthy and generally tolerating labor well, large variations in normal (minor protractions and arrests) will often correct themselves without intervention.
How is labor progress measured? Simply. There are really only 3 factors which can be reliably measured by the midwife or doctor when a woman is contracting to assess the progress of labor. They are DILATATION and EFFACEMENT of the cervical os, and DESCENT of the fetal head through the pelvis. The duration and frequency of contractions can also be measured (and less so, the intensity). However, the quality of contractions differs significantly between any two women in the ability to produce progress in labor.
Simply speaking (or maybe, over-simplistically speaking), labor can be divided into two phases, the latent phase and the active phase. During the latent phase of labor, the uterus is contracting, but a doctor or midwife usually cannot measure significant changes in the cervix over periods of time less than 2 or 3 hours (effacement moreso than dilatation). During the active phase of the labor, the cervix effaces and dilates, and in late active phase, the baby begins to descend through the pelvis.
When does the latent phase of labor begin?…..possibly days and weeks before the baby is born. Maybe latent phase labor is simply the increasingly noticable effects of prostaglandin-priming before the cervix measurably effaces and dilates.
The information most contracting women want to know is “WHEN will active phase begin?” The answer: “when latent phase is over”. That may sound flippant, but the preparatory process of latent phase labor is crucial in setting the stage for a successful, efficient active phase of labor. Many women feel as though they are in the active phase of labor when they are contracting frequently, even though they have not yet started to dilate. But that’s not what the doctors and midwives count as active labor, regardless of what it feels like to the laboring woman. Many women (especially first time mothers) will describe the length of their labor in terms of 20-30 hours. When dilatation of the cervix is used as the measurable indicator of active labor, their labor lengths are usually in the average range of 4-10 hours. This may be the first time that a mother’s work is under-appreciated and under-valued…….except by her. It probably won’t be the last time.
Over the course of the latent phase of labor, the os of the cervix slowly dilates to about 3-4 centimeters in diameter. This may take a first-time mother 6-20 hours of contractions, which are usually irregular in both frequency and intensity. Some women begin labor with the cervix already dilated to this point…….their prostaglandins have served them well. They have a jump start on labor, and generally these women’s labors progress very efficiently.
Once the cervix is about 4 centimeters dilated, and contractions are occurring regularly and intensely, the cervix dilates rapidly to about 9-10 centimeters. This is the active phase of labor. Once the cervix is almost completely dilated, progress slows a bit as the baby’s head begins to descend through the pelvis. Once at 4 centimeters, most women dilate about 2 centimeters per hour……first-time mothers a little more slowly, and experienced mothers sometimes much more rapidly. And there is a large variation in the range of this active phase progress. Generally, active phase is considered to be going too slowly if a first-time mother is dilating less than 1 centimeter per hour, or 1.5 centimeters per hour for an experienced mother.
The active phase of labor is further divided into three stages: First Stage, Second Stage and Third Stage. First Stage is that part of labor when the cervix is dilating. Second Stage is from full dilatation to the birth of the baby. And Third Stage is from the birth of the baby to the delivery of the placenta.